(a) Field of the Invention
The present invention relates to a poly(ethyleneterephthalate) (PET) tire cord, and a tire including the same. More particularly, the present invention relates to a PET tire cord that has high dimensional stability, and accordingly can increase riding comfort of a car, and a tire including the same.
(b) Description of the Related Art
Tire is a complex body of fiber/steel/rubber, and generally has a structure as illustrated in FIG. 1. Namely, the steel and the fiber cord take a role of reinforcing the rubber and form a basic skeletal structure in the tire. It is, so to speak, like a role of a bone in a human body.
As a reinforcement of the tire, the performances such as fatigue resistance, shear strength, durability, repelling elasticity, adhesion to a rubber, and the like are required to the cord. Therefore, various cords made of suitable materials are used according to the performances required to the tire.
Recently, rayon, nylon, polyester, steel, aramid, and the like are generally used as the materials for the cord, and the rayon and the polyester are used for a body ply (or a carcass) (6 in FIG. 1), the nylon is mainly used for a cap ply (4 in FIG. 1), and the steel and the aramid are mainly used for a tire-belt part (5 in FIG. 1).
The structure and the characteristics of the tire represented in FIG. 1 are briefly disclosed hereinafter.
Tread 1: A part contacting to the road surface; this part must provide a friction force necessary for braking and driving, be good in abrasion resistance, and also be able to stand against an external shock, and its heat generation must be small.
Body ply (or Carcass) 6: A cord layer inside the tire; this part must support a load and stand against a shock, and its fatigue resistance against bending and stretching movement during a driving must be good.
Belt 5: This part is located between the body plies and mostly composed of steel wire, and it lessens the external shock and also makes the ground-contacting surface of the tread wide and the driving stability good.
Side wall 3: A rubber layer between the lower part of the shoulder 2 and the bead 9; it takes a role of protecting the internal body ply 6.
Bead 9: A square or hexagonal wire bundle, wherein a rubber is coated on the steel wires; it takes a role of fitting and fixing the tire to a rim.
Inner liner 7: A part located inside the tire instead of a tube; it makes a pneumatic tire possible by preventing air leakage.
Cap ply 4: A special cord fabric located on the belt of a radial tire for some passenger cars; it minimizes the movement of the belt during driving.
Apex 8: A triangular rubber packing material used for minimizing the dispersion of the bead, protecting the bead by relieving the external shock, and preventing an air inflow during shaping.
Recently, developments for tires suitable for high-speed driving are required as the passenger cars gentrify, and accordingly the stability during high-speed driving and high durability of the tire are recognized as greatly important characteristics. Furthermore, the performance of the materials for the cap ply cord importantly comes to the force before everything else for satisfying the characteristics. In addition, the performance of the materials for the body ply cord is importantly raised as well, because the body ply inside the tire, that is the carcass, is the kernel of the reinforcement supporting the whole weight of the car and maintaining the shape of the tire.
First, the cap ply cord takes a roll of minimizing the movement of the steel belt in the tire. More particularly, the steel belt inside the tire is generally arranged in the oblique direction, the steel belt, however, tends to move toward the circumferential direction during high-speed driving, and there are some problems that the sharp ends of the steel belt may cause separation between the layers of the belt and shape deformation of the tire by cutting the rubber or generating cracks. The cap ply prevents the separation between the layers and the deformation of the shape of the tire and takes a role of improving the high-speed durability and the driving stability by restraining the movement of the steel belt.
A nylon 66 cord is mainly used for general cap ply cord. The nylon 66 cord may show the effect of restraining the movement of the steel belt by showing high shrinkage force at the stiffening temperature of 180 and wrapping the steel belt, however, a partial deformation may be occurred by the rapid change of temperature inside of the tire during driving and parking the car, or the load of the tire and the car, and it may clatter during driving and deteriorates the riding comfort of the car because of its low modulus and dimensional stability.
Meanwhile, the body ply takes a roll of supporting whole weight of the car and maintaining the shape of the tire. As a cord for the body ply, viscous rayon that is a regenerated fiber or nylon is mainly used, and recently the polyester-based materials is investigated and attempted to apply for the body ply material. Particularly, there are many-sided investigations for using the tire cord composed of the polyester-based materials to the body ply, because it has superior price competitiveness in comparison with the viscous rayon and the like, and can improve durability of the tire as well because of its high strength.
However, the tire cord composed of nylon or polyester-based materials has low dimensional stability against heat in comparison with the tire cord composed of cellulose-based materials, such as viscous rayon, and the like. Therefore, when the nylon or polyester-based tire cord is applied to the body ply, the shape of the tire may largely be deformed, and it becomes very difficult to maintain uniform tire shape. Particularly, the shape of the body ply or the tire may largely be deformed still more by the change of the temperature or the load caused during driving and parking the car, and it may largely affect the performance of the tire, in particular the riding comport of the car.